The use of 3D imaging techniques for exploring virtual representations of objects is known. For example, medical image data can be transformed into a 3D virtual representation of an organ, such as the colon, to allow a thorough examination of the region. In the case of conventional optical colonoscopy, the field of view available is generally directed only along the direction of navigation through the colon. As illustrated in FIG. 1, because of the folded nature of the colon lumen, this can result in a substantial portion of the colon not being visible during optical colonoscopy. Of course, in virtual colonoscopy, the viewer can change navigation direction and can also orient the virtual camera in any direction. While this flexibility allows the radiologist or other viewer to explore the entire surface of the colon, it is often difficult or impossible for a viewer to know whether a particular region has been explored. Thus, improved navigational aids would be desirable.
In addition to being used to view a virtual object, the 3D virtual environment can also be used to perform quantifiable analysis, such as distance and volume measurements in a region of interest. In present systems, such measurements generally involve the use of manually outlining a region for volume measurements. In addition, 3D ray-surface intersection have been used to perform length, diameter and angular measurements. Such techniques tend to be time consuming or computationally expensive. Thus, improvements for performing quantitative measurements in a virtual environment are desired.
An additional problem which is encountered during virtual examination is removing extraneous material from the object which is subject to examination. For example, in the case of virtual colonoscopy, it is necessary to remove stool and fluid from the colon to expose the surface of the colon wall. The traditional pre-imaging protocols for effecting colon cleansing are unpleasant and impose a deterrent to patients from obtaining such examination. Although electronic cleansing techniques are known, these techniques still encounter difficulties in properly removing material, such as in regions of intersection of two or more material types. Thus, improved electronic cleansing of a virtual object would be beneficial in such virtual examination applications.